Financial instruments and fair value measurement Financial Assets & Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Jun. 30, 2016
Derivatives
Liabilities:
Derivative Liability	$ 11,174	$ 13,028
Derivatives | Quoted Prices In Active Markets (Level 1)
Liabilities:
Derivative Liability	0	0
Derivatives | Significant Other Observable Inputs (Level 2)
Liabilities:
Derivative Liability	11,174	13,028
Derivatives | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative Liability	0	0
Equity Securities
Assets:
Investments	2,292	1,296
Equity Securities | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	2,292	1,296
Equity Securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Equity Securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Government bonds
Assets:
Investments	15,893	15,764
Government bonds | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	15,893	15,764
Government bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Government bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Corporate Bonds
Assets:
Investments	204,333	184,380
Corporate Bonds | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	204,333	184,380
Corporate Bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Corporate Bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Asset backed and mortgage backed securities
Assets:
Investments	3,300	8,746
Asset backed and mortgage backed securities | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	0	0
Asset backed and mortgage backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments	3,300	8,746
Asset backed and mortgage backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Derivatives
Assets:
Derivative Asset	18,333	25,303
Derivatives | Quoted Prices In Active Markets (Level 1)
Assets:
Derivative Asset	0	0
Derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivative Asset	18,333	25,303
Derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivative Asset	0	0
Fixed income mutual funds
Assets:
Investments	$ 405,508	$ 361,770